A jet-boat is a boat propelled by a jet of water ejected from the back of the craft. Unlike a powerboat or motorboat that uses a propeller in the water behind the boat, a jet-boat draws the water from under the boat into a pump-jet inside the boat, then expels the injected water through a nozzle at the stern.
Jet-boats are steered and maneuvered by directing the nozzle and water jet laterally from the longitudinal axis of the craft, such that the water jet both propels and steers the craft. Jet boats can be reversed and brought to a stop within a short distance from full speed using the jet.
A conventional screw impeller accelerates a large volume of water by a small amount, similar to the way an airplane's propeller accelerates a large volume of air by a small amount. In a jet-boat, pumping a small volume of water, accelerating it by a large amount, and expelling the water above the water line delivers thrust that propels the craft. Acceleration of the water is achieved by the impeller driven by a small ICE onboard the craft.